Optical modulators are devices that allow for the manipulation of a property of light, such as in an optical beam. This optical beam may be, for example, a laser beam. One type of optical modulator is an electro-absorption modulator (EAM) that is used for the transmitters in optical fiber communications. Other types of optical modulators include acousto-optic modulators, interferometric modulators, liquid crystal modulators, chopper wheals, fiber-optic modulators, and micromechanical modulators.
In the case of EAMs, these devices operate with lower voltages than other optical modulators, such as electro-optic modulators. They can also be operated at high speed. For example, a modulation bandwidth of tens of gigahertz can be achieved, making these devices useful for optical fiber-communications. An EAM can be integrated with a feedback laser diode, such as an electrically modulated laser (EML), on a single chip to form a data transmitter.
Typically, in the case of an EML with an integrated EAM, the laser will have a positive bias (voltage and current) while the modulator will have a negative bias (voltage and current). In such a situation, a negative power supply will be necessary. However, negative power supplies are not always readily available. Presently, bias circuits depend on negative voltage converters or regulators for generating reverse bias voltages for ground referenced EAMs, but this solution requires more parts, higher cost, more board space, and more direct current (DC) power consumption.